David Hockney takes us on an enthralling intellectual and visual journey as he rewrites the story of how the great drawings and paintings of the last six centuries were created. He demonstrates for the first time how artists as far back as the 15th century used mirrors and lenses to project colour images onto flat surfaces and then captured these projections in pencil and paint. As well as being the presentation of more than two years' research, Secret Knowledge is an amazing detective story, as Hockney uncovers piece after piece of scientific and historical evidence, each one revealing further secrets of the past.